Variable voice delay network control



1942- A. E. MELHOSE 2,300,798

VARIABLE voles DELAY NETWORK coumop Filed Aug. 31, 1940 4 Sheets-Sheet.l

PERFORATDR m/l/EA/Tok A E ME L HOSE A T TOR/VEV Nov. 3, 1942. A. E.MELHosE VARIABLE VOICE DELAY NETWORK CONTROL J 4 Sheets-Sheet 2 FiledAug 31, 1940 Nov. 3, 1942.

A. .E. MELHOSE- VARIABLE vows DELAY umwoax COMRCL Filed Au 31, 1940 4Sheets-Sheet 3 MM I Nov. 3, 1942.

A. E. MELHOSE 2,300,798 VARIABLE VOICE DELAY NETWORK CONTROL Filed Aug.31, 1940- 4 Sneets-Sheet 4 AMP.

DELAY? DCLAYZ SECTI DELAY! SEC:

DELAY! SECZ' lNl/A/TOR AEMELHOSE BY A T TORNEV Patented Nov. 3, 1942rgnr OFFICE VARIABLE. VOIC'E DELAY NETWORK CONTROL Alfred E. Melhose,Westfie'ld, N. J., assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application August 31, 1940,Serial No. 354,988

6 Claims.

This invention relates to communication systems and particularly to longline telephone systems where voice operated switching devices are used;

In such systems where the communication channel is normally conditionedagainst transmission of voice currents the incoming voice currents mustbe made to cause a switching action to take place so as to place thecommunication channel in the proper condition. Therefore, it is usual toinsert a voice delay circuit or network in the voice path to givesufficient opportunity for the switching to take place. If too littledelay is provided, then the switching does not occur soon enough and asmall part of the syllable or perhaps a whole syllable of the speechwhich has set the switching devices into operation is lost or clipped.Clipping is thus directly traceable to insufiicient delay. a

On the other hand, if too much delay is introduced the naturalness of atelephone conversation suffers since the listener cannot get animmediate response to his remarks. This effect is, of course, aggravatedby the so-called hangover time in the release of the talking circuit inthe opposite direction; It is, therefore, desirable to use a minimum ofdelay.

Other factors which afiect the amount of speech delay used are theaction of mutable links such as fading on transoceanic radio telephonecircuits and the talking habits or speech characteristics of differentusers of this type of apparatus. It is therefore usual to placesufii-cient delay in this type circuit to give good service under thepoorest conditions.

The object of the present invention is to improve operating conditionsby decreasing the amount of delay in the speech path to a minimum and tohave means for rapidly increasing this amount when clipping is noted.Therefore, a plurality of delay circuits or networks are provided andthese are controlled by switching means so that the amount of delay maybe varied at will. By way of example, the delay may be varied within arange of zero to approximately 40 milliseconds in steps of 4milliseconds each. The operating routine then is for the technicaloperator who is responsible for the continuous proper functioning of theapparatus to set the delay at a minimum value. When a distant operatoror monitoring operator notes clipping taking place, a report is made tothe technical operator, who thereupon makes an adjustment in the delaycircuits. According to routine the technical operator will reduce theamount of delay to the minimum or to the point where a minimum number ofreports of clipping are received. f

-A feature of the invention is an adjustable voice current time delaycircuit whereby the marginal time operation of the switching circuits atthe receiving end of a transmission channel may be maintained at aminimum point over a period including varying conditions tending todisturb such marginal time operation.

This invention is an improvement in the system disclosed in Patent2,207,720 granted upon the application of Cole et al., July 16, 1940.

The drawings consist of four sheets of circuit diagrams. With Figs. 1, 2and 3 placed together a circuit diagram of one terminal of aninterpolated telegraph and telephone system is shown.

Fig. 1 shows the transmitting telegraph circuits;

Fig. 2, partly schematic and partly circuit diagrams, shows thetelephone and controlling circuits;

Fig. 3 shows the receiving telegraph circuits; and

Fig. 4 isa detailed circuit diagram of the voice delay means indicatedby the rectangle H5 in Fig. 2 and fitted into the general diagram ofFig. 2 at the broken lines XX and YY.

One terminal of a system is shown but it will be understood that at somedistant point a similar terminal is located so that speech coming inover channel 20! will be transmitted from the radio transmitter 262 andits antenna 203to be received at the said distant point over the antenna2M and the radio receiver 285 for transmission into the speech path atthat point corresponding to the channel 26 I While speech is beingtransmitted from channel 20I over the antenna 2533, the telegraphtransmitting apparatus of Fig. 1 is inactive and the telegraph receivingapparatus of Fig. 3 at the distant point is similarly inactive. By thesame token, the telegraph transmitting apparatus of Fig. 1 at thedistant point and the telegraph receiving apparatus of Fig. 3 at thenearend as shown will be in operation.

In general, speech over channel 2M enters the hybrid coil 2% providedwith the usual balancing network 201, passes over path 268 through thenetwork 269 to the voice operated gain adjusting device (termed vogadfor short) 2. From the vogad 2H speech currents enter the hybrid coil2l2 where they split, part going on to the main speech channel and partentering the syllabic amplifier-detector 2B for control purposes. Theoutput of the amplifier-detector 2H3 feeds into the transmitting relaychain 214 which performs a variety of switching functions as will bemore clearly set forth hereinafter. At present it is sufficient to saythat the transmitting relay chain 214 clears the way for the speechcurrents to the antenna 203 and that the reception of this transmissionat the distant receiving terminal similarly conditions the receivingcircuits thereat for the proper reception of the speech currents. Themain portion of the speech currents passes from the-hybrid coil 212 intothe delay circuit 215 through a repeater 21% and the first transmittingsuppressor 2| 7. Thereafter the speech path is through privacy circuit2l8, the second transmitting suppressor'2l9 and another part of theprivacy circuit 22ii'to the hybrid coil 22!. Speech currents then passto the hybrid coil 22 2, thence to the transmitting repeater 223, andfinally to the radio transmitter 202.

At the distant receiving end the speech currents transmitted from theradio receiver 205 pass through the receiving repeater 224 and into thehybrid coil 225. At this point the control tone which accompanies speechis diverted through the control tone filter 226, to the receivingdetector 221 which operates the receiving relay chain 223. Thisreceiving relay chain responds to the control tone transmitted from thedistant end through the operation of the transmitting chain thereat, andlike the transmitting chain performs a variety of switching functionswhich will be more fully described hereinafter.

For the present it is sumcient to say that the receiving chain clearsthe way for the speech currents to reach the hybrid coil 288 and channel29!. The speech currents leaving the hybrid coil 225 enter the nexthybrid coil 229 and thence pass through a part of the privacy circuit230, the'first receiving suppressor 23!, another part of the privacycircuit 232 to the second receiving suppressor 233. From this point thespeech currents pass through the variable suppressor 234, a low-passfilter 235, a volume controller 236, a repeater 231, a network'238 andthence to the hybrid coil 2% from which they pass over the channel suchas 213! at the said distant terminal.

The functions of these various pieces of apparatus are briefly asfollows. The hybrid coil 206 receives Voice currents from the channel20! and transmits themoiit over the channel 288. The hybrid coil 2% alsoreceives voice currents from channe1'239 and transmits them out overchannel 28!. Actually the voice currents split equally to paths 2GBand239 but are prevented from passing over path'239 beyond the repeater237 by the unidirectional characteristics of this repeater. The functionof the balancing network 291 is well known. In this connection it shouldalso be noted that each of the hybrid coils H2, 22!, 222, 225 and 229 isprovided with an appropriate balancing network. The networks 299 and 238are provided to perform certain functions necessary in commercialtelephone circuits to compensate for the differences in transmissionwhen the channel 26! is connected to difierent types of telephonecircuits. Their inclusion or noninclusion in the system is immaterial tothe functioning of the apparatus comprising the present invention butthey are included in the schematic part of this disclosure in order torender the diagram as complete as possible. The vogad 2 I I is a meansfor adjusting the gain applied to the voice currents incoming thereto soas to provide a reasonably uniform level of output. The hybrid coil 2l2allows a small part of the voice currents to be taken off to thesyllabic amplifier-detector 2l3 without causing distortion in the voicecurrents flowing from the hybrid coil 2l2 to the rest of the circuit.The delay circuit 2 I5 is an arrangement by which voice currents aredelayed to allow time for the transmitting chain 2I4 to properly performits functions before the voice currents are finally delivered to theantenna 203. Since these delay circuits entail certain loss intransmission, amplifying means are associated therewith in the form of arepeater 216 which is a one-way amplifying repeater. The firsttransmitting suppressor ZITand the second transmitting suppressor 2l9both act to block speech currents therethrough when the relays cf thetransmitting chain are in their normal positions. When, however, thetransmitting chain is operated, the transmitting suppressor 2i! and thetransmitting suppressor 2|9 give a clear path for the transmission ofvoice. currents. The two privacy system units 218 and 220 are includedto render the speech between the antenna 203 and the distant antenna 254unintelligible, but do not form any essential part of the presentinvention, being again included for the purpose of rendering theschematic layout as complete as possible. The function of the hybridcoil 22] is to transmit to the hybrid coil 222 either speech coming fromthe privacy system unit 220 or telegraph signals coming from Fig. 1. Thefunction of the hybrid coil 222 is to pass on to the transmittingrepeater 223both the output of the hybrid coil 22! and the control toneoriginating from oscillator2 i0. This oscillator is a source ofalternating current of a frequency just outside of the voice range sothat it may be effectually filtered out at the receiving end withoutdisturbing the Voice currents entering the receiving circuit thereat.

Current from the oscillator, 24!! enters the control tone enabler 24!which is under the control of the transmitting relay chain 2M, as willappear. hereinafter. When the voice takes com-.

mand of the transmitting relay chain 2M and certain relays in thetelegraph transmitting apparatus of Fig. l are properly operated, thecontrol tone enabler 24I will allow alternating current from the source240. to enter the control tone compressor 242 and from this point thecontrol tone will be passed through the filter 243 to the hybrid coil222. The effect, therefore, is that when the voice takes command of thetransmitting relay chain 2l4 control tone at full volume will bedelivered to the hybrid coil .222. A short time thereafter, asmeasuredby the delay circuit 235 and controlled by a connection in thevoice path between thefirst transmitting suppressor 2H and the first.unit of the privacy system 2H2, the control tone compressor willoperate to reduce. the volume of the control tone being delivered to thehybrid coil 222 in inverse proportion to speech current volume.

The transmitting repeater 223 is a well-known type of one-way amplifier.The radio transmitter 202 and its associated antenna need no specialdescription. Likewise the radio receiver 205 and its associated antenna2114 need no special description. The repeater 224 is, like therepeaters 2l6, 223.and 231, a one-way amplifying device. The hybrid coil225 receives the output of the radio receiver 205. and allows part ,ofthis output to flow to thehcontrol tone filter .226 which deliversto.the receiving detector 22'! only the control tone.

205 to the privacy system units 230. and the various circuit unitsthereafter. During intervals of telegraph transmission the hybrid coil229 delivers the output of the radio receiver 205 to the telegraphreceiving apparatus of Fig. 3.

The privacy system units 230 and 232, like the privacy system units 220and 2I8, are used to insure secrecy in the transmission of intelligenceby translating for delivery to channel 20l the otherwise unintelligibletransmission from the antenna 203 to the antenna 204. The firstreceiving suppressor 23I and the second receiving suppressor 233, bothunder control of the receivingrelay chain 228, operate to block thespeech paths during those intervals when the control tone is absent fromthe transmission being received by the receiver 205. When the controltone is present as an indication that speech is present, the receivingrelay chain is operated and the receiving suppressors 23I and 233 give aclear path for speech currents toward the hybrid coil 206 and thechannel 20!. The variable suppressor 234 is a device used to cause thetransition from speech to silence and from si- 1 lence to speech to beslow so that clicks and unpleasant operations of the circuit will notdisturb the listeners. The low-pass filter 235 effectually blocks anycontrol tone which accompanies speech to this point and allows only thespeech to go into the volume controller 236.

At this point it should be noted that between the low-pass filter 235and the volume controller 236 there is a connection to the receivingdetector 221. Thus when the voice takes command at the distanttransmitting end, control tone from the oscillator 240 is transmitted bythe radio transmitter at full volume and this will enter the controltone filter 22B and the receiving detector 221 to insure the properoperation of the receiving master relay within the receiving relay chain228. By the time that the voice arrives, the receiving chain will haveconditioned the receiving circuit, particularly by operating the firstand second receiving suppressors 23I and 233 and the variable suppressor234. As the control tone is reduced in volume through the action of thecontrol tone compressor 242, voice current from the connection betweenthe low-pass filter 235 and the volume controller 236 will reach thereceiving detec tor 221 to augment the operation of this device andinsure the proper and continuous operation of the receiving chain evenduring periods when fading or other disturbances in the mutable linkcauses the receiving control tone to drop to a value where the continuedoperation of the receiving chain might be unsatisfactory.

That part of the circuit between and including radio transmitter 202 andradio receiver 205 is spoken of as a mutable link since it comprises asignaling channel capable of or liable to change from internal orexternal causewhich may give rise to interfering energy or morespecifically subject to noise, fading or change of attenuation. It is tobe understood, however, that the present showing is by way of exampleand that the term mutable lin does not necessarily mean that an operatinradio link is invariably involved but that the term is broader in itsmeaning and includes any channelliable to change from internal orexternal cause.

The volume controller 230 is a device generally under the supervision ofa technical operator for controlling the volume as indicated by amonitoring device, not shown, connected between this unit and thereceiving repeater 231. The receiving repeater 231 is, like the otherrepeaters 2I6, 223 and 224, a one-way amplifying device.

The syllabic amplifier-detector 2I3 is a device which will be unoperatedby the maximum noise which may be expected on the transmitting circuitbut will be operated quickly by speech signals of both high and lowamplitudes. It is connected to the hybrid coil 2l2 and delivers itsoutput to the transmitting relay chain 2M. If the receiving chain 228 isin its normal unoperated position, then the amplifier-detector 2I3 willbe enabled. If at this time voice currents come in over channel 20Itheir eifect' will be to operate the amplifier-detector H3 and thereuponto operate the transmitting chain 2M. The transmitting chain controlsthe transmitting suppressor 2H1, the privacy system unit 2I8 and, thesecond transmitting suppressor 2I0 as indicated by the lines extendingfrom the transmitting relay chain and ending in an arrow-head at thesedescribed units. Likewise, the transmitting chain controls the controltone enabler 24 I, this control extending through the armature and backcontact of relay I00 in the transmitting telegraph circuits shown inFig. 1. The transmitting relay chain 2M also controls the transmittingtelegraph ap paratus through a control extending to the back contact andarmature of relay I00, the resistance IN and the windings of relays I02and I03 to battery. The circuits are such that when the voice takescommand this latter circuit will be connected in the transmitting relay,chain to ground and hence relays I02 and I03 will be operated todisable the transmitting telegraph apparatus.

In like manner the receiving relay chain exercises its control over thereceiving suppressor 23!, the receiving suppressor 233 and the variablesuppressor 234. A connection extending to the syllabicamplifier-detector Z I3 indicates that the receiving relay chainoperates to disable the am-, plifier-detector 2 l3. A similar connectionextended to the vogad 2II indicates control of the vogad by thereceiving relay chain. Lastly, an other connection extended from therelay chain 228 to the telegrad 300 in Fig. 3 indicates control,

lay chain.

The transmitting telegraph apparatus consists,

generally, or a pair of tape transmitters I05 and Each of thesetransmitters has a series of I00. five contacts operating between aspacing battery lead I01 and a marking battery lead I08 and af fecting,in turn, the segments III to I20, inclusive, of the multiplexdistributor. This latter piece of apparatus consists, in general, of amotor and synchronizing equipment H0 operating a shaft I39. This shafthas upon it a number of brushes I2I, I22, I23 and I2d. The brush I2I asit passes successively over the segments I II to I 20, inclusive,connects these segments to the ring I25 which is connected througheither the armature and back contact of relay I26 or the armature andback contact of relay I21, thence through the back contact and armatureof relay I03 and the winding of the telegraph transmitting'line relayI28 to a point on a potentiometer consisting of the resistances I29 andI30 whereby the relay I28 will respond to .either marking or spacingpotential and thus ,operate its armature accordingly. When relay I28 isoperated by a spacing signal it closes a circuit through its armatureand contact to render, the telegraph tone enabler I3I ineffective totransmit telegraph tone from the source I32 to the hybrid coil 22 I Whenthe relay I28 is operated by a marking signal it opens this circuitwhich affects the telegraph tone enabler I3I in such a way thatalternating current from the source I32 freely passes to the hybrid coil.22I and thence out over the radio transmitter 202 and antenna 203.

It should be noted that when the transmitting relay chain 2I4 isoperated and, consequently, relay I03 is operated, that a connection isextended from spacing battery lead I01 through the front contact andarmature of relay I03 to the winding of relay I28 to hold this relayspacing and, therefore, continuously to block the transmission oftelegraph tone from the source I32 to the hybrid coil 22I.

The function of brush I22 is as follows: If the transmitting chainoperates at any time before brush I22 comes in contact with segment I33or segment I34, then relays I02 and I03 will be properly operated andfurther transmission of telegraph signals interrupted and the steppingof the tape magnet prevented. If, however, the operation of thetransmitting relay chain 2I4 occurs while brush I22 is on either ofthese segments I33 or I34, a connection will be extended from battery,ring I35 over brush I22 to segment I33 or I34, and thence through thewindings of relays I04 and I00, the back contact and armature of relay I02 to ground. This causes the circuit for the operation of relays I02and I03 to be opened to prevent the disabling of the telegraph apparatusfor this very short interval. This arrangement is provided so that ifthe voice takes command of the circuit at or during the transmission ofthe'last pulse of a telegraph code, this last pulse may be allowed to betransmitted without interruption.

The function of brush I23 is as follows. The segments and rings of thismultiplex distributor are developed for the sake of clarity and thebrush I23, now moving downwardly, has reached the point wheretransmission of the signals from the tape transmitter I06 has beencompleted. Brush I23 now establishes a connection from ground, ring I36,brush I23, segment I3'I, back contact and outer right-hand armature ofrelay I38, winding of stepping magnet I39, right-hand contact andarmature of relay I40 to battery. If relay I40 is on its right-handcontact, as it should be while this apparatus is operating normally, andthere is a sufficient supply of tape for use by the transmitter I06,then the magnet I39 will operate and advance the tape to the nextpunched character. As brush I23 advances it next comes into contact withsegment I4I where a connection is established from ground, ring I36,brush I23, segment I41, the contacts of the taut tape switch I42, whichwill be closed as long as there is sufiicient tape in this transmitter,to the left-hand winding of relay I38. This connection also extends inparallel through thenormal contacts and the inner makes before break orcontinuity contact of relay I38 through the right-hand winding of thisrelay, and these windings being opposed no operation of the relay I38will occur. If, however, upon the operation of magnet I39 the taut tapeswitch I42 had operated, then only the right-hand winding of relay, I38.would have been energized and this relay wouldthenhave operated andlocked through its inner right-hand armature to ground. This conditionwould have persisted until the taut tape switch I42 closed its contactsagain and brush I23 made contact with segment I4I whereupon the relayI38 would have been automatically released.

During the time that relay I38 is operated each of the segments I I6 toI20,;inclusive, would have been connected through the front contacts andleft-hand armatures of relay I38 to marking battery, so that a signalconsisting of five marking pulses would have been repeatedly sent eachtime the brush I25 ispassed over the segments II6 to I20, inclusive.

When brush I23 advances to segment I43 a connection is momentarilyestablished from ground, ring I36, brush I23, segment I43, the lowerwinding of relay I40 to battery. This tends to drive relay I40 to itsright-hand contact where it will remain unless some other circuit isclosed to change this condition.

As brush I23 advances further it first causes the operation of steppingmagnet I44 in a similar manner to the operation of stepping magnet I39.and attempts to operate the relay I45 and finally closes a circuit todrive relay I48 to its righthand armature.

The function of brush I24 is as follows: If during the time that brushI24 is on segment I4I relay I02 becomes operated, then a circuit will beestablished from ground, the armature and front contact of relay I02,ring I48, brush I24, segment I41, the upper winding of relay I46 tobattery. Relay I46 will thereupon be driven to its left-hand contactwhere it will remain until brush I23 drives it back to its left-handcontact. During the time that relay I46 is on its left-hand contact itwill cause the operation of relay I26 in an obvious circuit and therebyopen the transmitting circuit which operates the'telegraph transmittingrelay I28. When brush I24 reaches the lower segment I49 it will causethe relay I40 to move to its left-hand contact whereupon the relay I2'Iwill be operated and complete the opening of the circuit for relay I28.It will be noted that each of these relays I46 and I40 will beperiodically returned to its righthand contact at the ending of theperiod of activity of the other circuit, but if the telegraphtransmitting apparatus is now rendered ineffective, the relay willreturn to its lefthand contact immediately thereafter and before anysignals can be efiectively transmitted.

It should be noted before leaving the descriptionof the transmittingtelegraph apparatus that if both the taut tape switches open thelefthand windings of relays I38 and I45, respectively, that the contactsand the left-hand armatures of relay I45 are connected to spacingbattery so that first a series of five marking impulses and later aseries of five spacing impulses will be transmitted. This provides foran occasional transition betweena spacing and a marking impulsefor thepurpose of correcting the distributor speed at the distant end.

When the receiving relay chain 228 is in its normal unoperated conditionthen the telegrad 300 will be enabled. This will render the telegradeffective to operate the receiving telegraph apparatus. At this timetelegraph signals being received by the radio receiver are passed intohybrid coil229 and thence into the band-pass filter .30I from which.they are delivered to the telegrad 300. This results in the operationof relays 392, 303 and 334 to their marking contacts for each markingimpulse delivered to the telegrad 339. Relay 332 is known as thereceiving telegraph line relay and for each marking impulse itestablishes a ground connection to the ring 305. Relay 304 is known asthe corrector relay. Upon each spacing impulse this relay will cause itscondenser 303 to be energized and upon each marking impulse this relaywill deliver the condenser discharge into ring 391. Relay 333 is knownas the auxiliary relay and operates on each marking impulse to driveeither relay 338 or relay 399 to its left-hand contact, respectively.

The receiving telegraph apparatus consists, generally of two printers3H] and 3H and a multiplex distributor comprising a motor and certainsynchronous equipment 3l2 operating a shaft 3l3 carrying brushes 314,3l5, 3H5 and 3H.

As brush 314 moves downwardly it connects the ring 335 through segments3|8, 359, 323, 32| and 322 to the selecting magnets of printer 3! I andthereafter through segments 323, 324, 325, 326 and 321 to the selectingmagnets of printer 3l0. Thus for each marking impulse one of theselecting magnets of printer 3! i or printer 3H3 is operated.

Brush 313 in moving downwardly makes contact with segments 328 and then323 while brush 314 is traversing the connections to the selectingmagnets of printer 3| l. The segments 328 and 329 are associated withprinter 3H]. The con nection to segment 328 establishes a circuit fromground, ring 333, brush 3|6, segment 328, armature and contact of relay338 to the printing magnet 33L Thus the selection set up on printer 3!!!is rendered effective by the printing magnet 33! after the brush' 314has completely traversed the segments 323 to 327 and is now engaged inpassing over the segments 318 to 322. As the brush 3H5 advances it makesa connection from ground to segment 323, which leads to the lowerright-hand set of contacts of keys 332, for purposes which will behereinafter described.

As brush 3I6 next traverses segment 333 the printing magnet 334 will beoperated.

Brush 3!! makes contact from the ring 333 to the segment 336 during thetime that the brush 3E4 is traversing the segments associated with theprinter 3! I. extends a battery connection to the two windings of therelay 369 through the rectifiers 331 and 338. If this telegraphreceiving apparatus is now properly in operative condition there will bean open connection to theupper winding of this relay at the armature andcontact of relay 339. Any marking impulse coming in at this time will berendered efiective by the auxiliary relay 333 to keep relay 399 on itsleft-hand contact and thus render the printing magnet efiective. If, onthe other hand, the receiving relay chain 228 is operated by voicecurrents, then relay 339 will be released and ground on the armature ofrelay 339 will cause relay 333 to be driven to its other position wherethe circuit for printing magnet 334 is opened. Similar action of relay398 will take place when the brush 3! I traverses the segment 34 l Itwill also be noted that when the relay 339 is operated, as When thereceiving chain 228 is s in its normal position, thus denoting the factthat the receiving telegraph apparatus is effective, that relay 340 willbe operated. Relay 340 plays a particular role with relation to the key332.

If the distant telegraph transmitter corre- This circuit from ring 335sponding to transmitter 36 operates its taut tape switch so as to sendout a series of five marking impulses, then the receipt of these fivemarking impulses by the printer 3H1 results in a thumping of the printerwithout the production of any printing. If this becomes annoying to theoperator, then the key 332 may be moved to its right-hand position.Thereupon a circuit will be established from battery, the upperrighthand contacts of key 332, the Winding of relay 342, the lowerright-hand contacts of key 332 to the segment 329 and when brush 3";makes contact with segment 329 a connection is extended to ground onring 330. This causes relay 342 to operate and this relay locks up tobattery on its inner right-hand armature. Relay 342 is sufiiciently slowin releasing so that it will remain locked up in a manner now to bedescribed. Upon the first operation of relay 342 a circuit for theoperation of relay 343 is closed at the front contact and outerright-hand armature of relay 342. This relay now disconnects thesegments 323 to 32'! inclusive, from the selecting magnets of theprinter 319 and extends them to conductor 344 which, with the left-handcontacts of key 332 in their normal position, extends the groundconnection each time the brush 3 l 4 connects with a segment 323 to 321,inclusive, to the winding of relay 342 to maintain this relay operated.

If at the distant end the taut tape switch should return to normal, thenground impulses will not be supplied to the winding of relay 342 atsufficient intervals to keep this relay operated and it will thereforerelease and by releasing cause relay 343 to return to normal, so thatthe printer 3|!) again becomes efiective. the time that relay 342 islocked up the receiving telegraph apparatus is rendered ineffective bythe operation of the receiving relay chain 228, then relay 343 returnsto normal and this maintains relay 342 locked up until the telegraphapparatus is again rendered effectivethrough the operation of thereceiving relay chain 228.

The relay 342 may be unlocked at any time by moving the key 332 to itsleft-hand position.

As brush 3I5 moves it alternately makes contact with segments connectedto either conductor 345 or 343. These conductors are connected todifferent windings of the auxiliary corrector relay 341 and thereforethe discharge of the condenser 393 will tend to operate the relay 341 inone direction if the motor 3|2 is running fast or operate the relay 341in the other direction if the motor 3|2 is running slow. The correctingmeans is well known and will not be further described except to notethat a device 348, which will indicate fast or slow operation, isinserted at this point to indicate that correction may be properly made.I

The delay circuit 2H5 formin the principal feature of the presentinvention is shown in more detail in Fig, 4 which may be inserted in thegeneral schematic diagram at the lines XX and YY in Fig. 2. The pathfrom the hybrid coil 2l2 enters a filter 430 and from there passesthrough the contacts of keys 43!, 402, 493 and 404 to an amplifier 433before entering the repeater 2l6. Associated with each key is a delaycircuit network. Delay circuit 433 is associated with key 431, delay 43?is associated with key 432, delay circuit 438 is associated with key 433and delay circuit 439 is associated with key 434. With the keys in theirnormal position as shown all of the delay circuits are included in thespeech path. These delays are of various natures. That is,

If during 6 i I delay 488 will cause speech currents to be delayed for 4milliseconds, delay 491 will cause speech currents to be delayed 8milliseconds, delay 488 will cause speech currents to be delayed 8milliseconds and delay 489 will cause speech currents to be delayed 21milliseconds. Thus with the keys 4-0! to iii-ii as shown a total of 41milliseconds delay will be introduced into speech currents flowingthrough this circuit. By the operation of these keys in variouscombinations the delay may be varied from a value of 0 to the totalvalue of 41 milliseconds in steps of about 4 milliseconds each. Thus ifkey 39! alone is in the position shown a speech delay of 4 millisecondsWill occur. If key 4222 alone is in the position shown a speech delay of8 milliseconds will be involved. If keys dill and 492 are as shown andkeys M33 and 48 are operated, then a delay of 12 milliseconds will beprovided for. Other combinations of these keys will be apparent.

When the key dill, for instance, is operated then a compensating H-typenetwork comprising the resistances 4|!) to M4, inclusive, will beintroduced in the circuit in place of the delay network 4G6. Anamplifier 415 may be included in the circuit between the first threedelay circuits 406 to 408, inclusive, and the last delay circuit 489.

These keys 40! to 49 3, inclusive, are to be operated by a technicaloperator at this terminal.

Similar arrangements at the other distant terminal are provided Theoperation in general is to reduce the delay to a minimum amount. Whenclipping of speech is noted at one terminal, and this occurs frequentlyenough to be objectionable, the technical operator at the distantterminal is notified and he thereupon operates the keys 48! to 464 toinclude suflicient delay to overcome the difficulty. It has beenstandard practice heretofore to provide sufficient delay to provide goodoperation of the circuits under the most severe conditions which couldbe expected but this penalizes the circuit under favorable conditionsand hence, the variable delay is now provided and the method ofoperation established whereby the delay is reduced to minimum untilclipping at the distant end occurs.

What is claimed is:

1. In a communication system, a transmission channel normallyconditioned against the transmission of voice currents, voice operatedswitching means for conditioning said channel for the transmission ofvoice currents, a source of alternating current for transmission oversaid channel together with speech current under control of saidswitching means, and an adjustable delay circuit in the speech path fordelaying the voice currents whereby the relative times of the arrival ofthe said alternating current and the said voice currents at the distantend of said transmission channel may be controlled.

2. In a communication system, a, transmission channel, said channelincluding as a portion thereof and at the transmitting end thereof asplit circuit, means in one branch of said split circuit responsive tovoice currents for transmitting control tone comprising current from asource of alternating current to the distant end of said channel, andadjustable means in the other branch of said split circuit forcontrolling the relative times of the arrival at the distant end of saidchannel of said control tone and voice current.

3. In a communication system, a transmission channel, said channelincluding as a portion thereof and at the transmitting end thereof asplit circuit, said channel including as a portion thereof and at thereceiving end thereof a split circuit, a source of control tone, meansin one branch of said transmitting split circuit responsive to voicecurrents for connecting said source of control tone for transmission ofcontrol tone over said transmission channel, means in one branch of saidreceiving split circuit for blocking transmission from said channelbeyond that point, means in the other branch of said receiving splitcircuit responsive to control tone for operating said blocking means toallow voice currents to freely pass said point and adjustable means inthe other said branch of said transmitting split circuit for delayingthe transmission over said channel until said control tone has beenconnected for transmission over said channel and said blocking means hasbeen operated thereby.

4. In a communication system, a transmission channel normallyconditioned against the transmission of voice currents, voice operatedswitching means for conditioning said channel for the transmission ofvoice currents, a source of alternating current for transmission oversaid channel with speech under control of said switching means, delaycircuits in the speech path for delaying the voice currents forcontrolling the relative times of the arrival of the said alternatingcurrent and the said voice currents at the distant end of saidtransmission channel and means for varying the number of said delaycircuits included in said speech path.

5. In a communication system wherein telegraph signals are interpolatedin telephone conversations durin lulls and pauses therein, telegraph andtelephone circuits at the transmitting and receiving terminals of thesaid system, a transmission channel extending from each transmittingterminal to each distant receiving termi-- nal, switching means foralternatively connecting said telegraph and said telephone circuits tosaid channels, each said channel being normally switched for thetransmission of telegraph signals, voice operated means at thetransmitting end of each said channel for operating the said switchingmeans thereat and for connecting a source of control current to the saidchannel, means at the receiving end of each of the said channelsresponsive to control current for operatin the said switching meansthereat, voice current delay circuits at the transmitting end of eachsaid channel for delaying the transmission of voice currents over thesaid channels for a predetermined period after said control current hasbeen connected thereto and means for varying the length of saidpredetermined period.

6. A transmission path including a switching device having twoalternative positions, a delay circuit of substantial electrical delaycharacteristics and a compensating network having impedancecharacteristics equivalent to those of the delay circuit and ofrelatively negligible delay characteristics in combination with contactson the switching device alternatively in two positions thereof forconnecting the delay circuit or the compensating network into thetransmission path.

ALFRED E. MELHOSE.

